Selective laser melting or laser sintering is an additive layering process by which pulverulent, in particular metallic and/or ceramic raw materials can be processed to three-dimensional work pieces of complex shapes. To that end, a raw material powder layer is applied onto a carrier and subjected to laser radiation in a site selective manner in dependence on the desired geometry of the work piece that is to be produced. The laser radiation penetrating into the powder layer causes heating and consequently melting or sintering of the raw material powder particles. Further raw material powder layers are then applied successively to the layer on the carrier that has already been subjected to laser treatment, until the work piece has the desired shape and size. Selective laser melting or laser sintering can be used in particular for the production of prototypes, tools, replacement parts or medical prostheses, such as, for example, dental or orthopaedic prostheses, on the basis of CAD data.
An apparatus for producing moulded bodies from pulverulent raw materials by selective laser melting is described, for example, in EP 1 793 979 A1. The prior art apparatus comprises a process chamber which accommodates a plurality of carriers for the shaped bodies to be manufactured. A powder layer preparation system comprises a powder reservoir holder that can be moved to and fro across the carriers in order to apply a raw material powder to be irradiated with a laser beam onto the carriers. The process chamber is connected to a protective gas circuit comprising a supply line via which a protective gas may be supplied to the process chamber in order to establish a protective gas atmosphere within the process chamber. The protective gas circuit further comprises a discharge line via which protective gas containing particulate impurities such as, for example, residual raw material powder particles and welding smoke particles may be withdrawn from the process chamber.